Electrodeposition of silver



Patented Apr. 5, 1938 UNITEDSTATES PATENT OFFICE ELECTRODEPO SITION F SILVER Alan Richard Powell and Emyr Conwy Davies,

London, England, assignors to Johnson, Matthey & Company, Limited, London, England,

I a British company No Drawing.

Application October 5, 1936, Se-

' rial No. 104,149. In Great Britain January 26,-

9 Claims.

This invention relates to the electrodeposition of silver and has for its main object to provide a plating bath from which hard bright deposits of sliver of any desired thickness can be obtained.

Present practice in silver plating irom cyanide It is well known that the addition of organic sulphides, such as carbon disulphide, to the normal plating bath tends to produce smoother and brighter deposits of silver but the advantages to adopted.

It is also well known that silver plating baths containing excessive amounts of free alkali metal cyanide produce very hard matt deposits which are diflicult and costly to polish. For this reason the amount of free alkali metal cyanide is usually kept down to the minimum required for satisfactory plating.

We have now found that the advantageto be obtained by the use of organic sulphides selected from the group carbon disulphide and mereaptans which are soluble in the bath, in respect to brightness of deposit and the advantage of increased amounts of free alkali metal cyanide as regards hardness of deposit can be combined and considerably enhanced by the further addition to the normal plating bath of a colloidal solution of a detergent. fication and claims means an alkali metal salt of a soap-forming acid, such as a monobasic saturated or unsaturated carboxylic or hydroxycarboxylic acid of the aliphatic series containing not less than eight carbon atoms in the molecule, or or an alkali metal salt of a sulphonic acid derived from one of thessaid soap-forming acids or from the corresponding alcohol. The addition made to a cyanide bath to produce a bright silver plate may thus consist of any of the commercial forms of soap, including sulphonated soaps. All

these compounds tend to hydrolyze in solution with the production 01 a'srnall quantity of the free acid in a colloidal form which appears to be adsorbed to a small extent by the deposit, thus producing a fine-grained structure consisting of When the bath is made up with soft water, about 0.1 ounce of soap per gallon is sumcient, but when made up with hard water more is required since part is converted into the corresponding The term detergent in the specicalcium or magnesium compound which forms a silky precipitate and gives the bath an opalescent appearance which, however, does not interfere with the production of bright silver plates. A small quantity of glycerine or of 'a glycol may be added to the bath to reducestill further the grain size of the deposit. Obviously, the soap may be produced in situ in the bath by the addition of free acid,as for example sulphonated acid in the form commonly known as Turkey red oil.

Deposits obtained from the improved baths according to this invention are much harder than have a brilliant white lustre which requires little or no polishing. There are therefore no losses of silver due to polishing and silver plating costs are consequently very substantially reduced.

The free alkali metal cyanide content of the plating bath may vary within wide limits, for example from 1 to 16 ounces per gallon, with corresponding effects upon the hardness of the deposited silver.

The sulphide brightening solution is added to the plating solution from time to time as required. This brightening solution is prepared by saturating a portion of the plating liquor or-alternatively an alkali metal cyanide solution with carbon di-' sulphide and returning the sulphide solution obtained to the plating bath" The following examples will further illustrate how the said invention'may be carried out in practice, but the invention is not restricted to these examples.

' Example 1 Silver (as KA (CN)z) 0 Free potassium cyanide 8.0

Turkey red oil 0.75

Sulphide brightening solution (obtained as described above) Example 2 A bath is prepared as follows:-

Ounces per gallon Silver (as KA(CN):) 3.0 Free potassium cyanide 6.0 Castile soap (sodium oleate) 3.0

Sulphide brightening solution (obtained as described above) 0.75

The baths described are preferably operated at room temperature and with a current density between 1 and 8 amperes per square foot. Higher current densities tend to produce burnt deposits.

What we claim 1. A processior the electrodeposition of silver, in the form of hard bright deposits requiring those obtained in the ordinary silver bath and little or no polishing, from an alkali metal cyanide bath comprising an alkali metal argento-cyanide,

acids derived from the alcohols corresponding to said aliphatic acids.

2. A process for the electrodeposition 01 silver, in the form of hard bright deposits requiring little orno polishing, from an alkali metal cyanide bath comprising an alkali metal argento-cyanide, an excess of tree alkali metal cyanide and an organic sulphide of the groupconsisting of carbon disulphide and mercaptans which are soluble in the bath, which consists in adding to the said bath a commercial soap, including sulphonated soaps.

.3. In the process 01' electrodepositing silver from a bath comprising an alkali metal argentocyanide, an excess of free alkali metal cyanide, an organic sulphide of the group consisting of carbon disulphide and mercaptans which are soluble in the bathand an alkali metalsalt oi an acid of the group consistingoi aliphatic acids containing no lessthan eight carbon atoms in the molecule, sulphonic acids derived from said aliphatic acids, and sulphonic acids derivedi'rom carbon disulphide and mercaptans which are;

soluble in the bath and an alkali metal salt of an acid oi the group consisting oi aliphatic acids containing no less than eight carbon atoms in the molecule, sulphonic, acids derived from said aliphatic acids. and sulphonicacids derived from the alcohols corresponding to said aliphatic acids,

the step of introducing the organic sulphide in v the form of a sulphide brightening solution prepared by saturating an alkali metal cyanide solution with carbon disulphide and returning the sulphide solution to the plating bath.

- I l A E oFco Ecr1oN.= vPatent llO- 2,113,517; H I I I V A QHARojrowsLL -Er AL,

sisting of carbon disulphide and mefcaptans' soluble in the bath, and an alkali metal salt of an acid of the group consisting of aliphatic acids containing no less than eight carbon atoms in the molecule, sulphonic acids derived from said aliphatic acids, and sulphonic. acids derived from the alcohols corresponding to said aliphaticacids.

6. A plating bath comprising a potassium argento-cyanide, an excess of freepotassium cyanide, carbon disulphide and Turkey red oil.

'7. A plating bath comprising a potassium argento-cyanide, an excess of free potassium cyanide, carbon disulphide and commercial sodium oleate (castile soap).

8. A process for the electrodeposition of silver, in the form or hard bright deposits requiring little or no polishing, from an alkali metalcya+ nide bath comprising an. alkali metal argentocyanide, an excess of tree metal cyanide, and an Y organic sulphide'ot the group consisting oi. carbon disulphide and mercaptans soluble in the bath, which consists} in adding to the said batli an alkali metal salt of an acid of the group consisting of aliphatic acids containing no less than eight carbon atoms in the molecule.

9. A process for the electrodeposition of silver in the form of hard bright deposits requiring little or no polishing,'irom an alkali metal cyanide bath comprising an alkali metal argentocyanide, an-excess oi free alkali metal cyanide,

and an organic sulphide of the'group consisting of carbon bisulphide and mercaptans which are soluble in the bath, which consists in adding to the said bath a colloidal solution of an alkali metal salt 01" a soap forming acid which tends to hydrolize in solution with the production of a small quantity of the free acid in a colloidal form which appears to be adsorbed to a small extent by the deposit, thus producing a fine grained structure consisting 01 almost subarthroscopic;

..crystals. said soap forming acidwbeing selected from the group consisting of monobasic saturated or unsaturated carboxylic or hydroxycarboxylic acids of the aliphaticseries containing not less than eight carbon atoms in the molecule, sulphonic acids derived trom the said aliphatic acids, and sulphonic acids derived from the alcohols corresponding to said aliphatic acids.

Y ALAN RICHARD POWELL.

mumv com DAVIES.

m1; $."la.

. It is "hereby certified that error appears "the printed specificationcl or the above mniibered' patent requiring correction as roiiows Page-1'," second '-col.umn,. line 9-, beroretheword "acid' 'ineert ricinoleicgandthat the said I Letters Patent shouldbe read wit-ih-thzls correctiontherein that the same my man to the recordhor the-case '11; the Patent'0ffice.

Signed a sassins 51st day arm a." Dr; 1958;

(Sealilierry llan ,n-of Patents,

little or no polishing, from an alkali metal cyanide bath comprising an alkali metal argento-cyanide,

acids derived from the alcohols corresponding to said aliphatic acids.

2. A process for the electrodeposition 01 silver, in the form of hard bright deposits requiring little orno polishing, from an alkali metal cyanide bath comprising an alkali metal argento-cyanide, an excess of tree alkali metal cyanide and an organic sulphide of the groupconsisting of carbon disulphide and mercaptans which are soluble in the bath, which consists in adding to the said bath a commercial soap, including sulphonated soaps.

.3. In the process 01' electrodepositing silver from a bath comprising an alkali metal argentocyanide, an excess of free alkali metal cyanide, an organic sulphide of the group consisting of carbon disulphide and mercaptans which are soluble in the bathand an alkali metalsalt oi an acid of the group consistingoi aliphatic acids containing no lessthan eight carbon atoms in the molecule, sulphonic acids derived from said aliphatic acids, and sulphonic acids derivedi'rom carbon disulphide and mercaptans which are;

soluble in the bath and an alkali metal salt of an acid oi the group consisting oi aliphatic acids containing no less than eight carbon atoms in the molecule, sulphonic, acids derived from said aliphatic acids. and sulphonicacids derived from the alcohols corresponding to said aliphatic acids,

the step of introducing the organic sulphide in v the form of a sulphide brightening solution prepared by saturating an alkali metal cyanide solution with carbon disulphide and returning the sulphide solution to the plating bath.

- I l A E oFco Ecr1oN.= vPatent llO- 2,113,517; H I I I V A QHARojrowsLL -Er AL,

sisting of carbon disulphide and mefcaptans' soluble in the bath, and an alkali metal salt of an acid of the group consisting of aliphatic acids containing no less than eight carbon atoms in the molecule, sulphonic acids derived from said aliphatic acids, and sulphonic. acids derived from the alcohols corresponding to said aliphaticacids.

6. A plating bath comprising a potassium argento-cyanide, an excess of freepotassium cyanide, carbon disulphide and Turkey red oil.

'7. A plating bath comprising a potassium argento-cyanide, an excess of free potassium cyanide, carbon disulphide and commercial sodium oleate (castile soap).

8. A process for the electrodeposition of silver, in the form or hard bright deposits requiring little or no polishing, from an alkali metalcya+ nide bath comprising an. alkali metal argentocyanide, an excess of tree metal cyanide, and an Y organic sulphide'ot the group consisting oi. carbon disulphide and mercaptans soluble in the bath, which consists} in adding to the said batli an alkali metal salt of an acid of the group consisting of aliphatic acids containing no less than eight carbon atoms in the molecule.

9. A process for the electrodeposition of silver in the form of hard bright deposits requiring little or no polishing,'irom an alkali metal cyanide bath comprising an alkali metal argentocyanide, an-excess oi free alkali metal cyanide,

and an organic sulphide of the'group consisting of carbon bisulphide and mercaptans which are soluble in the bath, which consists in adding to the said bath a colloidal solution of an alkali metal salt 01" a soap forming acid which tends to hydrolize in solution with the production of a small quantity of the free acid in a colloidal form which appears to be adsorbed to a small extent by the deposit, thus producing a fine grained structure consisting 01 almost subarthroscopic;

..crystals. said soap forming acidwbeing selected from the group consisting of monobasic saturated or unsaturated carboxylic or hydroxycarboxylic acids of the aliphaticseries containing not less than eight carbon atoms in the molecule, sulphonic acids derived trom the said aliphatic acids, and sulphonic acids derived from the alcohols corresponding to said aliphatic acids.

Y ALAN RICHARD POWELL.

mumv com DAVIES.

m1; $."la.

. It is "hereby certified that error appears "the printed specificationcl or the above mniibered' patent requiring correction as roiiows Page-1'," second '-col.umn,. line 9-, beroretheword "acid' 'ineert ricinoleicgandthat the said I Letters Patent shouldbe read wit-ih-thzls correctiontherein that the same my man to the recordhor the-case '11; the Patent'0ffice.

Signed a sassins 51st day arm a." Dr; 1958;

(Sealilierry llan ,n-of Patents, 

